Solved

c++ Nullable implementation

Posted on 2009-07-08
3
1,773 Views
Last Modified: 2012-06-27
Do you know a good c++ implementation of the Nullable Generic in c#?
Something like Nullable<class T>

Is there a good way to avoid using the .Value member to get the value?
Nullable<float> Number;
 
float x=Number.Value; //Can I avoid the '.Value' here somehow? and use x=Number? without custom casting staff?

Open in new window

0
Comment
Question by:Hanochr
3 Comments
 
LVL 40

Accepted Solution

by:
evilrix earned 250 total points
ID: 24802668
Not being a C# expert and going just by the docs I think something like below (with a few tweaks maybe) will model the behavior you are after.

>> Is there a good way to avoid using the .Value member to get the value?
I've overloaded operator *()

template < typename T>
class Nullable
{
public:
   Nullable(T * p = 0)
      :p_(p)
   {
   }
 
   bool HadValue() const
   {
      return p_ != 0;
   }
 
   T const & Value() const
   {
      return *p_;
   }
 
   T & Value()
   {
      return *p_;
   }
 
   T const & operator * () const
   {
      return *p_;
   }
 
   T & operator * ()
   {
      return *p_;
   }
 
   T * p_;
 
private:
};
 
int main()
{
   bool b = true;
 
   Nullable<bool> bnYes(&b);
   Nullable<bool> bnNo;
}

Open in new window

0
 
LVL 53

Assisted Solution

by:Infinity08
Infinity08 earned 250 total points
ID: 24802720
I see evilrix already posted his suggestion. Mine's slightly different, so I'll post it too (it's a rough example, just to give an idea).


>> Is there a good way to avoid using the .Value member to get the value?

An overloaded cast operator like below should do the trick.
#include <iostream>
 
template <class T>
class Nullable {
  private :
    T data;
    bool null;
 
  public :
    Nullable(T d) : data(d), null(false) { }
    Nullable() : data(), null(true) { }
 
    bool hasValue() { return !null; }
    T value() { return data; }
    
    operator T() { return data; }
};
 
int main(void) {
  Nullable<float> numberA = Nullable<float>(5.0);
  Nullable<float> numberB = Nullable<float>();
  
  (numberA.hasValue()) ? (std::cout << numberA.value()) : (std::cout << "NULL"); std::cout << std::endl;
  (numberB.hasValue()) ? (std::cout << numberB.value()) : (std::cout << "NULL"); std::cout << std::endl;
  
  float value = numberA;
  std::cout << value << std::endl;
  
  return 0;
}

Open in new window

0

Featured Post

Free Tool: Subnet Calculator

The subnet calculator helps you design networks by taking an IP address and network mask and returning information such as network, broadcast address, and host range.

One of a set of tools we're offering as a way of saying thank you for being a part of the community.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

Introduction Hi all and welcome to my first article on Experts Exchange. A while ago, someone asked me if i could do some tutorials on object oriented programming. I decided to do them on C#. Now you may ask me, why's that? Well, one of the re…
The article shows the basic steps of integrating an HTML theme template into an ASP.NET MVC project
The goal of this video is to provide viewers with basic examples to understand and use pointers in the C programming language.
The goal of this video is to provide viewers with basic examples to understand how to create, access, and change arrays in the C programming language.

830 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question